if you're having problems with mirroring, there's a good chance the problem is network related. not to mention, mirroring isn't the greatest option. as by design it will sacrifice quality to keep the image in sync
what are you trying to mirror?
if it's files, look at
beamer, beamer is basically a video player with airplay output. so you start a file playing on your mac, and it shows up on the aTV.
another option is
Plex once you get everything organzed, just leave the server running, and select files on the aTV. Plex has an aTV4 app, or on the 3, there is an secondary program called plex-connect that will replace the content in the trailers app with all of your plex content.
both of these will give you good image, as the transcoder is able to read ahead on the file, instead of having to wait till the image is played on your computer screen, and then converting in real time to send to the aTV.
if it's web content in a browser, you can improve it a bit, but it will always be a bit jerky at times.
make sure you have the fastest network you can. keep in mind everything is on your network twice, once from the computer to the router, and then again from the router to the aTV, so it can overload a slow network very quickly. Try hardwiring either your laptop or the aTV, to take some strain off the wireless side of your network.